why the output of ad9129 has very large harmonic?

I'm debugging ad9129' s output for several days, and the output wave is so strange, it can't be used, why?

But i have checked the my circuit with the reference design of ADI, also i measured power supply of ad9129 on my board. also emi  filter  to power supply. using external 2.8G clock source as reference clock to ad9129.

 i powered on it, and config the register according section of "start-up sequence" of the AD912 datasheet 。On the board, using xilinx V7 FPGA lvds port to driver AD9129,setting DDS output frequence to 200MHz or other value.  

i find the DAC has wave ouput . But using the oscilloscope measure, it can see wave have jitter. using spectrum to measure, the output have larger harmonic wave.

so who can help me to resolve the issure. thank you very much.

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  • +1
    •  Analog Employees 
    on Aug 18, 2018 12:05 AM

    In order for us to better understand the problem, we need to take a look at your schematic design. It seems to me there is something wrong with the input clock. Can you use a clean external clock and feed the DAC and FPGA off of that?

    Also, you mentioned that the DDS frequency is set to 200MHz but the large spur that you are talking about is sitting at 700MHz which is not a harmonic of this signal! You may need share more information or contact one of our local FAEs to help you out.

Reply
  • +1
    •  Analog Employees 
    on Aug 18, 2018 12:05 AM

    In order for us to better understand the problem, we need to take a look at your schematic design. It seems to me there is something wrong with the input clock. Can you use a clean external clock and feed the DAC and FPGA off of that?

    Also, you mentioned that the DDS frequency is set to 200MHz but the large spur that you are talking about is sitting at 700MHz which is not a harmonic of this signal! You may need share more information or contact one of our local FAEs to help you out.

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